In particular, this invention relates to the detection of conducting metal target objects situated in environments which, through their own magnetic and electrical properties, interact with the fields transmitted by metal detectors and thence or otherwise the detection apparatus of such a detector. A consequence of the intimate physical proximity of a target object with such an environment is that the magnetic signal from the target object has hitherto been difficult to distinguish from the background magnetic signals produced by the said environment using any of the metal detectors currently available and/or described. The difficulty of detection and discrimination in such an environment increases when the electrical and magnetic properties of the target objects vary greatly between instances of the target objects, as is usually the case.
The environments previously alluded to provide significant magnetic reactive and/or resistive components in their transmitted fields, as well as providing temporally quasi-static fields which can induce signals in a detector as it moves through spatial variations in those quasi-static fields.
The object of this invention is to produce a method and apparatus by which greater sensitivity to metallic target objects can be achieved in such difficult environments.